Among the earliest accounts of the anatomy of _Lepidostrobus_ are those by Hooker[415] and Binney[416]. One of the specimens described by the former author (fig. 190) affords an interesting example of an unusual manner of fossilisation; a hollow stem or _Lepidodendron_ is filled with sedimentary material containing several pieces of _Lepidostrobi_ in an approximately vertical position. [Illustration: FIG. 190. _Lepidodendron_ stem with _Lepidostrobi_. (After Hooker.) A. Side-view showing leaf-cushions on the left-hand side and the _Knorria_ condition on the right. B. View of transverse section; _s_, sections of _Lepidostrobi_.] The fact that _Lepidostrobi_ usually occur as isolated specimens renders it impossible in most cases to refer them to particular species of _Lepidodendron_. Neither external features nor anatomical characters afford satisfactory criteria by which to correlate vegetative and fertile shoots; in some measure this is due to the imperfection of our knowledge as regards the range of structure within the limits of species; it is also due to lack of information as to the extent to which the transition from sterile to fertile portions of a shoot is accompanied by anatomical differences. Prof. Williamson wrote: “I have for many years endeavoured to discover some specific characters by which different _Lepidostrobi_ can be distinguished and identified, but thus far my efforts have been unsuccessful[417].” In a few cases, such as those mentioned in the description of _Lepidodendron Veltheimianum_ and _L. Wünschianum_, it has been possible to correlate cones and vegetative shoots. The most complete account we possess of the anatomy of _Lepidodendron_ cones is that by Mr Maslen[418], who first demonstrated the occurrence of a ligule on the sporophylls, and thus supplied a missing piece of evidence in support of the generally accepted view as to the homology of the sporangium-bearing members and foliage leaves. i. _Lepidostrobus variabilis_ (Lindley and Hutton). 1811. “Strobilus,” Parkinson, Organic Remains, Vol. I. p. 428, Pl. IX. fig. 1. 1828. _Lepidostrobus ornatus_, Brongniart, Prodrome, p. 87. 1831. _L. variabilis_, Lindley and Hutton, Foss. Flora, Pls. X. XI. 1831. _L. ornatus_, Lindley and Hutton, Foss. Flora, Pl. XXVI. 1837. _L. ornatus_ var. _didymus_, _Ibid._ Pl. CLXIII. 1850. _Arancarites Cordai_, Unger, Genera et Spec. Plant. foss. p. 382. 1875. _Lepidostrobus variabilis_, Feistmantel, Palaeontographica, Vol. LXIII. Pl. XLIV. 1886. _L. variabilis_, Kidston, Cat. Palaeozoic Plants, p. 197. 1890. _L. ornatus_, Zeiller, Flor. Valenciennes, p. 497, Pl. LXXVI. figs. 5, 6. —— _L. variabilis_, Zeiller, Flor. Valenciennes, p. 499, Pl. LXXVI. figs. 3, 4.